1. Field of the Invention
The present invention relates to power equipment, including but not limited to mowers, tillers, snow blowers, and tractors, and more particularly, to a variable speed transmission and method for using the variable speed transmission.
2. Discussion of Related Art
Conventional power equipment such as lawn mowers, snow blowers, mulchers, etc. often include “self-propulsion” mechanisms for automatically driving the wheel, track or other drive mechanism used to propel the power equipment. Typically, the self-propulsion drive mechanism is activated by engaging a transmission that connects/disconnects the transmission shaft to the drive wheel. The speed of the drive wheel varies proportionally with the speed of the engine. Accordingly, the speed of the drive wheel can only be varied by changing the throttle position or by changing the gear ratios inside the transmission to increase/decrease the speed of the engine.
Recently it has become desirable to provide all types of power equipment with variable speed transmissions in order to smoothly vary the drive speed of the power equipment without increasing/decreasing engine speed to vary the drive speed. One attempt at providing such a device is currently incorporated in power equipment produced and sold in Europe by France Reductor, Inc. Idler pulley systems have also been used in an attempt to provide variable speed power equipment.
The France Reductor VST includes a first belt that is attached between a drive pulley on the engine output shaft and a driven pulley on a rotational shaft. A second pulley is attached to the same rotational shaft as the driven pulley and is locked and rotates synchronously with the driven pulley. A second belt is attached between the second pulley and a second driven pulley connected to a transmission shaft. The transmission shaft is connected to a transmission that transmits rotational power to a drive wheel or other drive mechanism. A clutch located in this transmission can be actuated to engage/disengage the transmission and transmit/disengage rotational power to the drive mechanism.
In order to vary the speed of the drive mechanism, a plate supporting the rotational shaft can be moved against the bias of a spring to tension and loosen the first belt and second belt, respectively. The first driven pulley and the second drive pulley (both of which are located on the same rotational shaft) have variable width grooves that are caused to vary when their respective belts are tensioned and loosened. Accordingly, when the first belt is tensioned, the first belt moves deeper into the groove of the first pulley towards the rotational axis of the rotational shaft, thus rotating the rotational shaft at ever increasing speeds as tension in the belt increases. Likewise, when the second belt is simultaneously loosened, the groove in the second drive pulley becomes narrower and the second belt moves out of the groove and away from the rotational axis of the rotational shaft, thus increasing the speed of the second belt and ultimately increasing the speed of the drive mechanism. Two belts are required in such a system to provide the necessary increase in variable speed output for the power equipment drive mechanism. In addition, two control mechanisms are necessary such that one control mechanism can actuate the transmission and one control mechanism can vary the speed of the transmission.
Because the France Reductor VST system requires two belts, four pulleys, two control mechanisms and a separate clutched transmission, the cost of the system and the space requirements are both relatively high. It is usually necessary to mount this VST system on top of a housing structure in order to fit such a large system on power equipment. In addition, the many different parts make the system susceptible to mechanical failures and creates problems with the range of aesthetic design available to power equipment that incorporates such a system. Furthermore, the actuation of the system is a two step process, and speed variation can be sudden at times if the transmission and the variable speed actuation mechanisms are not actuated in the correct order. The belts are also constantly moving in this related art VST system.
Another type of VST system that is commonly used in power equipment includes a hydrostatic transmission for varying the speed output to a drive unit. In such a system, a single control mechanism can be used to vary the speed of a drive unit from a neutral position to maximum speed. However, such transmissions are relatively expensive to manufacture. In addition, maintenance and repair of such a system are significantly more difficult and expensive than maintenance and repair of belt drive and/or geared transmission systems.